The invention relates to a method and transmission control system for operating a multi-clutch transmission.
The present invention also relates to a transmission control system, computer program product and a storage medium for a computer all to be used with a computer for executing said method.
Automatic and semi-automatic mechanical transmission systems for vehicles are well known in the prior art. Typically, such systems comprise a multi-speed mechanical change gear transmission, at least one friction clutch drivingly interposed the engine and the transmission and a central processing unit or controller for receiving input signals from sensors and issuing command output signals to actuators for operating the transmission.
An automatic/semiautomatic transmission skip shift, i.e., a direct shift of more than one ration step, is also known in the prior art e.g. U.S. Pat. No. 4,576,065.
In a multi-clutch transmission such as dual clutch transmission (DCT), power-shifting may be preferred in most situations.
In certain vehicular operating conditions with a vehicle equipped with a DCT, the vehicle operator may command a skip shift from the previously engaged gear ratio to a desirably engaged ratio. Typically, skip up-shifts are demanded in those situations wherein the vehicle is relatively lightly loaded, travelling on a flat ground or downhill and when powerful vehicle acceleration is performed. This is due to the fact that in such conditions, the engine speed after a power-up-shift can be higher than or near the up-shift speed, leading to a short time between successive upshifts and an increase in number of gear shifts. The skip shifts are used in order to avoid a series of rapid single up-shifts by shifting directly into a desirable lower gear ratio (higher gear). Such skip-shifting strategy may prolong the clutch life and increase the driving comfort.
A corresponding vehicular operating condition can occur when a vehicle is driven in a road condition, such as a steep uphill and heavy vehicle, where the vehicle travel resistance is very high, that is, a DCT would rapidly perform several successive power down-shifts. The same problem with increased clutch wear and decreased driving comfort would be the result.
Skip shifting may be actuated by, for example, pressing a skip shift button by the vehicle operator. Due to other tasks facing the operator of the vehicle, the skip shift button may not be actuated at all or at a wrong time, thereby obviating the benefits of having the skip shift function at all. The problem with the system described above is that it puts the burden on the operator to actuate the skip shift button. DE102005028551 discloses a method for operating a multi-clutch transmission drivingly connectable to a prime mover provided in a vehicle for propulsion.
It is desirable to provide an improved method and device for controlling a multi-clutch transmission without contemporaneous input from the vehicle operator.
In a first aspect of the invention it is provided a method for operating a multi-clutch transmission drivingly connectable to a prime mover provided in a vehicle for propulsion, said method comprising the steps of:                providing a control unit for managing at least the prime mover and the transmission,        providing a prediction model comprising at least one simulated shift sequence for said transmission, characterized in that said method further comprising the steps of:        predicting the time between a first power upshift and a second power upshift or a first power downshift and a second power downshift for said transmission by using said at least one prediction model,        modifying at least one parameter for operating the transmission if the predicted time between said first power upshift/downshift and said second power upshift/downshift for said transmission is shorter than a predetermined time limit.        
The method is characterized in that said parameter for operating said transmission is modified by performing at least one of the following steps:                lowering said first shift speed limit;        increasing said second shift speed limit,        
and where said shift speed limits are only allowed to be modified to a maximum extent where said prime mower still remains within a maximum torque range for said prime mower.
According to a further embodiment of the invention said method further comprising the step of providing information about engine rpm, vehicle speed, an accelerator position, and road information to said control unit.
In another embodiment of the invention said predetermined time limit is shorter than 1 second.
In a further embodiment of the invention said predicting of the time between a first upshift/downshift and a second upshift/downshift is performed by a real time simulation by said control unit.
In another embodiment of the invention said first power upshift/downshift and said second power upshift/downshift are successive power shifts.
In a further embodiment of the invention said parameter for operating said transmission is a first shift speed limit for said first power upshift/downshift and a second shift speed limit for said second power upshift/downshift.
In a further embodiment of said embodiment a two or more steps of a conventional up-/downshift is selected if said predicted time is longer than said predetermined time even though said shift speed limits have been modified to said maximum extent.
In another embodiment of the invention said parameter for operating said transmission is at least two shift sequences. In a further embodiment of this mentioned embodiment said at least two shift sequences comprise one of:                a sequential power up-shifting and a two or more steps of a conventional upshift,        a sequential power down-shifting and a two or more steps of a conventional downshift.        
In a still further embodiment said two or more steps of a conventional up-/downshift is selected if said predicted time with said first power upshift and said second power upshift or said first power downshift and said second power downshift is shorter than said predetermined time limit.
There is also provided a transmission control system comprising a control unit arranged for controlling a multi-clutch transmission, characterized in that said control unit is programmed to perform the steps of the first mentioned method embodiment.
The advantage of the invention is better travelling comfort and a decreased clutch wear.